Conventional torque applying tool handles must meet certain basic needs. The handle must bond well to a steel component, such as the shank of a screwdriver. It must be strong enough to withstand the forces and torque applied to the tool. At the same time, the handle must also provide appropriate ergonomics so that a user of the tool may comfortably and securely hold the tool. To achieve a balance between the strength, bonding and comfort of use, tool handles made from two or three shots of plastic are available on the market. Each shot represents a single step in the molding process and is a complete or partial layer forming part of the handle. For example, several varieties of tool handles with two or three shots of material are commercially available. One such type of two shot tool handle has an inner layer of polypropylene and an outer layer of thermoplastic rubber to provide a gripping surface. Another type has a polypropylene layer of one color and a second polypropylene layer of another color. The two layers provide a color pattern and are used, for example, to provide information such as manufacturer brand name.
A commercial three shot handle has an inner polypropylene layer, a second polypropylene layer which covers over the inner layer and an outer thermoplastic rubber layer which covers most of the second layer and provides a gripping surface. For use in a chisel, a three shot handle has been made with two shots of cellulose acetate butyrate and a shot of urethane to provide a gripping surface. The urethane covers a portion of the cellulose acetate butyrate shots, but a portion of those layers remains visible.
Additionally, a three shot handle with two polypropylene layers and a thermoplastic rubber shot is available. The second polypropylene shot is partially visible and the thermoplastic rubber shot provides a gripping surface over a portion of the outside of the handle. In producing the molded plastic handles of the prior art, a determining factor in the cycle time is related to the amount of cooling time necessary before the cycle can be completed by removing the molded structure from the mold.
Based upon the prior art described above, it appears that a saturation point as to the maximum number of layers that is cost-effective has been reached. Nevertheless, there is always a need for cost-effectiveness in the production of commercial products such as the torque applying tools to which the present invention is directed.